1. Technical Field
The present invention relates to a process for distillation of thermo-sensitive liquid hydrocarbon products, in particular the residue drawn off from the bottom of an atmospheric distillation column of a crude petroleum refinery
The invention relates equally to an apparatus for performing the process.
2. Background Art
In known crude petroleum refineries, the residue is drawn off at 320.degree. to 350.degree. C. from the bottom of an atmospheric distillation column and is delivered into a furnace where it is heated to a temperature of the order of 390.degree. to 410.degree. C. This temperature corresponds to the maximum allowable value that will avoid all thermal deterioration (e.g., coking).
The product leaving the furnace is delivered into a large diameter manifold (1 to 1.5 m) in which it partially vaporizes before being introduced into a vacuum distillation column having a diameter of the order of 6 meters, the pressure in the upper part of this column being maintained at about 20 mm of Hg. The product introduced into this column flash vaporizes into a zone where the pressure is of the order of 40 to 60 mm Hg.
The applicants presented themselves with the problem of vaporizing the largest possible portion of this residue so as to minimize the undistilled quantity of the residue. To achieve this, it is necessary to heat the residue to the highest possible temperature without triggering a thermal deterioration of the product at the minimum pressure in the vacuum distillation column.
Now, the furnace used to heat the residue already operates under limiting conditions with regard to cracking (temperature equal to 390.degree. to 410.degree. C., pressure of the order of 1 bar). Moreover, the transfer manifold actually used for transferring the product leaving the furnace into the vacuum distillation column and in which occurs a large part of the vaporization of the product by reducing the pressure from about 1 bar to about 0.2 bar, does not act either to heat the product or to separate the liquid and gaseous phases.
French Patent Document No. 2,323,423, assigned to SPIE-BATIGNOLLES, describes a process for heating the petroleum crude before its introduction into the atmospheric pressure distillation column of a petroleum refinery. This process uses a succession of steam heated exchanger separators in series. This succession of exchanger separators provides gaseous phases which are introduced at different levels into the atmospheric distillation column, thereby promoting distillation while avoiding unnecessary overheating of the product.
This process of heating by steam is not always adapted to the vacuum distillation of a petroleum and chemical product that is sensitive to thermal deterioration in view of the level of the temperatures involved.